a.What advantages does ligroin have over n-pentane as a recrystallization solvent?
b. What advantages foes ethanol have over n-octanol as a recrystallization solvent?
3 answers
Doesn't it make a difference as to what we are recrystallizing?
"Like dissolves like"...ligroin and n-pentane are nonpolar solvents (saturated hydrocarbons), and therefore have no significant advangtage over each other in terms of ability to dissolve various materials, although one might be stronger. The same is the case for ethanol and n-octanol, although those are alcohols rather than saturated hydrocarbons, yet the same argument applies. DON'T take my words as absolute though, I am an undergrad in my first semester of O-Chem and this is to the extent of my knowledge. It is sound however from what I've read, because again disregarding their relative strengths in the two questions, both solvents being compared are limited to the same range of solutes that they are able to dissolve with respect to one another.
Common sense dictates that crystallization of a compound can only occur if the compound that you're trying to crystallize is a crystalline solid. Crystalline solids are generally polar molecules that can freely interact with neighboring molecules to form a lattice (a uniform, geometric distribution of like molecules). Keep this in mind while I answer your question.
1) ethanol vs octanol - Ethanol is a better crystallization solvent because of two main factors. First, octanol is much more lipophilic than ethanol. This means that octanol likes lipids more than ethanol. And since lipids are not crystalline solids but, rather, waxy solids at best, octanol is the poorer solvent of the two to use for crystallization. Ethanol, on the other hand, is the better alcohol to use in crystallization because it is better at dissolving polar compounds that are less lipophilic and more crystalline in nature. Reason #2: 1-octanol, with a bp of 195 degrees C, is much more difficult to remove than ethanol when drying a cyrstalline solid... By David M
1) ethanol vs octanol - Ethanol is a better crystallization solvent because of two main factors. First, octanol is much more lipophilic than ethanol. This means that octanol likes lipids more than ethanol. And since lipids are not crystalline solids but, rather, waxy solids at best, octanol is the poorer solvent of the two to use for crystallization. Ethanol, on the other hand, is the better alcohol to use in crystallization because it is better at dissolving polar compounds that are less lipophilic and more crystalline in nature. Reason #2: 1-octanol, with a bp of 195 degrees C, is much more difficult to remove than ethanol when drying a cyrstalline solid... By David M
2 answers